Stucco over painted block,
brick

Ask the pros-August, 2006By Reggie Bullard

Stucco
over painted
block, brick or stucco by chipping the block

Chipping up the wall is a variation of an old
method
that seems to work
the best for us. Sand blasting is a real chore
and not cheap. Usually,
sandblasting leaves a dust cloud that looks
like a fire in the
distance.

Here
paint is chipped off using a chipping
hammer. A good place to
buy these is from Harbor Freight. Deep
holes don't matter. They have a
better key for the mortar.

A
race between a hatchet and an electric
chipping hammer shows the
hatchet is almost as fast. It is good
to have a grinder on the job to
sharpen
the hatchet or bits once in a while.

Ready for mortar. Chips
leave areas both rough and porous
for a permanent
bond.

Flex
con is
used for additional adhesion.
We mixed flex con half and half with
water and mixed it into the dry
mixed mortar.
I have to advertise also forMilestone.
Milestone
"E" chemical is concentrated
and will make the equivalent of 3
buckets of flex con, diluted with
water.
The acrylic not only is adhesive for a
good bond, but is resistant
to cracks and
adds strength.

Here
the dry mix is mixed with the wet mix
with a drill, but a hoe
works, too.

Scratch
coat is applied with a lot of pressure
to give a good squish
into the holes. Scratch coat is scored
and allowed to set 2 days before
the brown coat. How long will this
last? I think about
4,000 years.

Paint on bonding agents seem to fail over
time, At least all the work
we
have done with them on the outside (over
painted surfaces) eventually popped
off the wall. The
reason paint on agents fail on the outside of
a building is because
they
dissolve in water. The reason they work to
begin with is that the
surface
dissolves when wet plaster or cement mortar is
applied. The mortar then
mixes with the bonder and dries together,
forming a chemical
bond.
We have had a lot
of cracks nailing metal lath over the painted
block. I think the reason
we have excessive cracking with lath is the
paint forms a “slip joint”.
The stucco expands and contracts one way and
the block or brick another
way, causing a lot of cracks. Nailing lath on
block is also a slow and
expensive process. Even with stub nails or pin
set pins the lath
doesn't
seem to be attached as well as putting the
mortar right on the block.
Nailing
brick is unreliable. The nails break
up the brick, leaving the only resort of
driving nails into the
mortar joints.
Most of the
area of the block is chipped up, leaving the
pores open on the blocks
for
a good bond. A few holes don't
hurt, mortar squished into
these
holes form a good key for the slab. We have
had very few or no cracks
at
all using this method.